This multicentric, randomized, double-blind and controlled study aims to examine the effect of a fermented dairy product containing the probiotic Lactobacillus casei DN-114 001 (Actimel® = tested product) on the incidence of respiratory and gastro-intestinal common infectious diseases (cumulated number of infections during the intervention period: primary criteria), and on the Quality of Life in adults submitted to multi-stressor situation. Volunteers received either 200g/day of tested product (N=121) or control product (N=118) for 7-weeks.